Arrangement for preventing the skidding of wheels of a motor vehicle

ABSTRACT

Each wheel has a pulse generator which furnishes a pulse sequence having a repetition rate depending upon wheel speed. The pulses set a monostable multivibrator, whose output, after low pass filtering and differentiating causes the furnishing of an output signal indicative of skidding when the rate of change of the repetition rate exceeds a predetermined rate of change.

United States Patent 15 3,696,270 Schnaibel et al. Oct. 3, 1972 [5ARRANGEMENT FOR PREVENTING THE SKIDDING OF WHEELS OF A [56] ReferencesCited MOTOR VEHICLE UNITED STATES PATENTS [72] Inventors: EberhardSchnaibel; Helmut 3 522 973 8/l970 Klein et al 303/21 g m? 22 3f3,184,606 /1965 Ovenden m1 ..303/21 bet won an h 3,572,848 3/1971Marouby ..303/21 schirieberdin i 3,494,671 2/1970 Slavin etal. ..303/21Stu an an 5, German 3,499,689 3/1970 Carp et a1. ..303/21 g y 3,558,1971/1971 Lueck et al ..303/21 [73] Assignee: Robert Bosch GrnbH,Stuttgart, Germany v Primary Examiner-Kenneth H. Betts [22] Filed: July6 1970 Attorney-Mmhael S. Stnker [21] Appl. No.: 52,171 [57] ABSTRACTEach wheel has a pulse generator which furnishes a Foreign ApplicationPriority Data pulse sequence having a repetition rate depending uponwheel speed. The pulses set a monostable mul- July 1969 Germany 977'6tivibrator, whose output, after low pass filtering and differentiatingcauses the furnishing of an output [52] US. Cl. ..317/5, 180/82, 303/21CG, signal indicative of skidding when the rate of change 180,105 E ofthe repetition rate exceeds a predetermined rate of [51] Int. Cl. ..Bt8/08 change [58] Field of Search ..303/21; /105, 1; 317/5;

340/262, 263 19 Claims, 8 Drawing Figures l T I 45 1 1 13 Z PATENTEnum 3I972 3.696. 270

M1 mu fhe/r Ar TO/P/VEV ARRANGEMENT FOR PREVENTING THE SKIDDING OFWHEELS OF A MOTOR VEHICLE BACKGROUND OF THE INVENTION This inventionrelates to an arrangement for generating an output signal indicative ofskidding of wheels of a motor vehicle. In particular, it relates to sucharrangements whereinthe wheels of the motor vehicle have associatedtherewith signal generating means which furnish signals whose repetitionrate is a function of a rotational speed of the wheel. Connected withthe signal generating means are logic circuit means which furnish theoutput signal indicative of skidding when the rate of change ofrepetition rate of the signal sequence exceeds a predetermined orpermissible rate of change. This invention relates to an arrangementwherein excessive wheel skidding may be detected substantially withoutdelay. I

When brakes are applied to a moving motor vehicle, care must be takenthat the wheels are not blocked so that they slide rather than rotatealong the path. The coefficient of friction between a sliding wheel andthe surface on which it is moving is substantially lower than thecoefficient of friction between a rolling "wheel and the surface uponwhich it is moving. A wheel will always be blocked when the force to betransmitted from the wheel to the road surface which is generatedthrough the pressure between the brake shoe and the drum or disc exceedsthe maximum possible static friction force which is proportional to thecoefiicient of friction between the wheel and the surface and theloading upon the wheel. A blocking of the wheel should of course beprevented for reasons of safety since the whole vehicle may otherwise besubject to skidding.

When the brakes are applied to a vehicle moving along a straight path,the deceleration of the vehicles causes the rear wheels to be unloadedwhile the load is transferred to the front wheels. Therefore, to preventblocking of the rear wheels, the brake force applied to the rear wheelsmust be less than the brake force applied to the front wheels.

The above-mentioned problems which appear during a braking of a vehiclecan also appear when driving force is applied to the wheels of thevehicle. For vehicles moving directly on the road surface, sliding ofthe drive wheels can start a skidding of the vehicle, while the sameprocess in a vehicle moving along tracks can cause unnecessary timedelays during acceleration of such vehicle.

Systems are known which control the application of brakes to the wheelsin dependence on excessive decelerations in the turning of the wheel.Such an excessive deceleration in rotational speed of the wheel isindicative of the beginning of a skidding process. Further, electricalsignal generators are known in which the relative movement between aflywheel mass and the drive shaft of the wheel causes the closing of acontact under conditions of excessive acceleration or deceleration.

These known arrangements have the disadvantage that the element whichmeasures excessive acceleration or deceleration has contacts which aresubject to wear. Further, these arrangements have time constantsassociated therewith which do not allow the beginning of a skiddingprocess to become immediately effective in controlling the braking orthe driving power applied to the wheels.

SUMMARY OF THE INVENTION It is an object of this invention to furnish anarrangement for generating an output signal in the event of a probableskidding of a motor vehicle. It is a further object of this inventionthat such an arrangement work without contacts which are subject to wearand substantially without time delay.

This invention is an arrangement for furnishing an output signal in theevent of a probable skidding of the motor vehicle. It comprises signalgenerating means operatively associated with at least one wheel of thevehicle. These signal generating means furnish a signal sequence whereinthe time interval between sequential signals corresponds to therotational velocity of said wheel. Logic circuit means are operativelyassociated with said signal generating means. The logic circuit meansfurnish an output signal when the change in said time interval exceeds apredetermined change depending upon the rotational velocity of saidwheel. The logic circuit means comprise a first multivibrator and a lowpass filter connected to the output of said multivibrator.

The arrangement in accordance with the present invention is particularlyeffective, when a differentiating stage is connected to the output ofthe low pass filter. The differentiating stage may for example comprisean operational amplifier which has an input capacitor and a feedbackresistance.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a motor vehicle equippedwith an arrangement in accordance with this invention;

FIG. 2 shows one embodiment of signal generating means;

FIG. 3 shows a block diagram of one embodiment of the present invention;

FIG. 4 is a block diagram of an arrangement for blocking the operationof the arrangement in accordance with FIG. 3 for low vehicle speeds;

FIG. 5 shows a number of voltage-time curves at different points of thearrangement of FIG. 3;

FIG. 6 is a block diagram of another embodiment of the presentinvention;

FIG. 7 shows a number of voltage-time curves at selected points in thearrangement of FIG. 6; and

FIG. 8 shows a differentiating stage for use in an arrangement accordingto FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of thepresent invention will now be described with reference to the drawing.

FIG. 1 shows a wheel of a vehicle, numbered 11, which rolls on thesurface of a street, 12. The wheel 11 is connected to the axle l3.Mounted on axle 13 is a brake disc 14. A brake cylinder arrangement 15is operatively connected with disc 14 by means of a linkage 16 on whichare mounted the brake shoes 17. The signal generating means are denotedby symbol 18 and have a mechanical input connected to the axle 13. Logiccircuit means 19 are connected with an electrical output of signalgenerating means 18. The output of the logic circuit means is connectedwith a first input of the brake cylinder arrangement 15. A secondinputof said brake cylinder arrangement is connected to the output ofbrake control means 21. Brake control means 21 may for example comprisea pressure cylinder. In this case the connection between the brakecontrol means 21 and the brake cylinder arrangement 15 may be a hosewhich conducts the pressure fluid. The brake control arrangement 21 isconnected to the brake pedal 23,

for example by means of an additional linkage. The

brake pedal 23 is connected with the chassis of the motor vehicle and ismovable relative to said chassis.

If the driver of the vehicle which contains the arrangement described inFIG. 1 desires to apply the brake, he depresses pedal 23. The brakepedal movement is transmitted via linkage 22 and the brake controlarrangement 21 to the wheels of the vehicle. Specifically, brake poweris applied to disc 14 via brake cylinder arrangement 15, linkage 16 andbrake shoes 17. The wheel 11 is therefore decelerated via axle 13. Wheel11 may block if the brakes are applied too rapidly. The wheel will thencease rolling along surface 12 and will instead slide. This sliding maycause the vehicle to skid. Signal generating means 18 which may forexample be pulse generating means now generates pulses, the intervalbetween pulses depending upon the rotational velocity of the wheel 1 1.If the rate of change of this time interval exceeds a predetermined rateof change, logic circuit means 19 furnish an output signal to brakesignal arrangements 15 which causes a decrease in the power transmittedfrom brake shoes 17 to brake disc 14.

FIG. 2 shows one embodiment of signal generating means for use in thearrangement of this invention. A wheel 26. is connected to axle 13. Thiswheel is constructed of ferromagnetic material and has a number ofprojections along its circumference, as for example teeth 27. A yoke 28extends around a part of the circumference of the wheel. This yoke mayfor example be substantially U-shaped and may have legs each of which ispositioned either opposite a tooth 27 or opposite gap between saidteeth. A magnetizing current flows through a coil 29 mounted on yoke 28.The inductivity of coil 29 varies in accordance with the position ofwheel 26, that is, in dependence upon whether or not the magneticcircuit is closed via yoke 28, teeth 27 and wheel 26 or whether theairgap is relatively large because of the space between the teeth. As thewheel 26 turns under yoke 28, the inductivity of coil 29 varies therebyinducing an alternating current in coil 29. The so generated alternatingcurrent components are available at terminals 31 and 32 in FIG. 2. Ofcourse, other pulse generating means may be used. For example wheel 26may have a number of magnets 27 of alternating polarity affixed to itscircumference. Magnets 27 may be mounted on a wheel made of any type ofmechanically suited material. Alternatively, wheel 26 may be made ofmagnetic material and magnets are induced along the circumference. Ayoke 28 again extends over magnets 27 in this case in such a manner thatwhen one leg of the yoke is opposite a magnet of a given polan'ty thesecond leg is opposite a magnet of the opposite polarity. An air gapexists between the legs of yoke 28 and the magnets. A coil 29 is mountedon yoke 28. If wheel26 now turns under yoke 28, alternatingly positiveand negative voltage pulses may be derived from terminals 31 and 32. Therepetition rate of the pulses will increase with increasing rotationalspeed of wheel 26.

An alternative embodiment'of pulse generating (signal generating) meansmay be optical means. The path of light from a light source toaphotoelectric element may be periodically interrupted by projections ona wheel such as wheel 26 of FIG. 2. The intermittent light falling onsuch a photosensitive element will cause the generation of a pulsatingcurrent, the time interval between pulses again depending upon therotational speed of wheel 26. The rotational speed of wheel 26 of coursehas a predetermined fixed relationship to the tangential speed of wheel1 1.

The block diagram shown in FIG. 3 shows the signal generating means suchas those shown in FIG. 2 in block 18. The output of signal generatingmeans is connected to the input of a Schmitt trigger 34 whose output isconnected with additional differentiating means 35. The output ofdifferentiating means 35 is connected with an input of firstmultivibrator means, here a monostable multivibrator 36. Connected tothe output of monostable multivibrator 36 are low pass filter means,here a low pass filter 37 whose output is connected with a feedbackcircuit having an integrating characteristic and denoted by referencenumeral 38. A second input of integrating feedback circuit 38 isconnected to a block 39 which denotes means for furnishing a referencesignal to feedback means 38. The output of integrator means 38 isconnected to a second input of monostable multivibrator 36. A signalapplied to this second input causes variations in the time in whichmonostable multivibrator 36 is in the unstable state. Blocks 38 and 39both are part of additional circuit means for furnishing adifferentiated signal corresponding to the derivative with respect totime of the low pass filter output. The output of low pass filter 37 isfurther connected to the input of threshold means via an amplifier 41.The threshold means are denoted by reference numeral 42 and actuallyhave two outputs, one connected to the set and another to the resetinput of second multivibrator means, here a monostable multivibrator 43.The output of one side of the monostable multivibrator 43 is connectedto one input of a coincidence stage 44. The second input of coincidencestage 44 is obtained from a terminal 45, the signal applied to whichwill be discussed below. The output of coincidence stage 44 is furnishedvia an amplifier 47 to terminal 46 and constitutes the desired outputsignal of this invention. A terminal 48 is connected to the output ofintegrating means 38.

The signal furnished at terminal 45 mentioned above is derived asfollows: Reference is made to the circuit of FIG. 4 which shows an ANDgate 51 having a plurality of inputs 48, 48', etc. The output of ANDgate 51 is connected to the input of an amplifier 52 which maypreferably be a Schmitt trigger circuit. The output of amplifier 52 isconnected to a plurality of terminals 45 45', etc.

Schmitt trigger 34. These pulses are differentiated by thedifferentiating means 35. The output of the differentiating means 35comprises a sequence of pulses having the shape shown in line 135 ofFIG. 5. The pulses shown in line 135 trigger monostable multivibrator36. The output of monostable multivibrator 36 is filtered by the lowpass filter 37. The output of low pass filter 37 is a substantiallysteady signal corresponding to the time average value of the pulsesshown in line 136 of FIG. 5, namely the output pulses of monostablemultivibrator 36. Under condition of a moving vehicle to which no brakesare being applied, the output voltage of monostable multivibrator 36(136) and the output of low pass ,filter 37 (137) are shown towards theleft side in FIG. 5, The average value as depicted in line 137 isapplied to t'he input of integrating means 38. .A constant butadjustable reference voltage is applied to the other input ofintegrating means 38 via a reference source 39. The output ofintegrating means 38 is applied to monostable multivibrator 36 in such amanner that the time interval in which the multivibrator 36 is in theunstable state is adjusted in such a way that the onoff time of pulsesin sequence 136 remains substantially constant. Thus under steady stateconditions the time average 137 of pulse sequence 136 does not dependupon the rotational velocity of wheel 11. However, the more rapidly thefrequency of the signal generated by signal generating means 118changes, the further integrator 38 lags in main-taining the constanton-off ratio of monostable multivibrator 36 and thus the time average137 of the output voltage of monostable muldeceleration, the outputvoltage 137 of low pass filter 37 will begin to decrease.

This decrease in voltage is amplified in amplifier 41. If the wheel 11is decelerated sufficiently, the decrease will exceed the predeterminedor permissible value (minus b). In this case the lower threshold valueof threshold means 42 has been passed. Thus threshold means 42 furnishan output signal which triggers multivibrator 43. This monostablemultivibrator is adjusted to remain in the unstable state for apredetermined time, for example, 200 milliseconds. This output voltageis shown in line 143 of FIG. 5. It is applied to coincidence stage 144and, via an amplifier 47, may be applied to a magnetic valve which isnot shown in the Figure. This magnetic valve will then cause a decreasein pressure in the brake cylinder arrangement 15 causing the brakes tobe lifted from wheel 11.

If no further deceleration of the wheel takes place at this point, thevoltage 137 remains constant and monostable multivibrator 43 remains inthe unstable state wherein a pulse is furnished to coincidence means 44.If the wheel is now accelerated due to reduction of 6 sliding, outputvoltage 137 of low pass filter 37 again increases, thus causing theupper threshold of threshold means 42 (+b) to be crossed. The thresholdmeans 42 then furnish a second output which switches mul- -.tivibrator43 back to its original state, thereby terminating the pulse applied tocoincidence means 44. The threshold means 42 may for example comprise afirst and second operational amplifier each constructed in such a mannerthat it switches for a different input level. Such operationalamplifiers generally have a feedback resistance which furnishes apositive feed back. This causes the operational amplifier to switch whena predetermined voltage is applied at its input.

Alternatively of course two Schmitt triggers might be used.

This termination of the pulse generated by monostable multivibrator 43is shown clearly in line 143 of FIG. 5. The magnetic valve controllingthe brake pressure is now reset to its original state via coincidencemeans 44 and amplifier 47 causing brake power to be reapplied. It isseen that threshold means 42 returns the monostable multivibrator 43 toits reset state prior to the time that it would normally have returnedthereto.

However, if the sliding wheel 11 is not accelerated sufficiently inspite of the loosened brakes, as can happen on an icy street, then thedistance between pulses furnished by monostable multivibrator 36 doesnot decrease as mentioned above and the output voltage 137 of low passfilter 37 does not increase sufficiently. Thus the upper threshold valueof threshold means 42 (+b) is not reached. In this case the return ofmonostable multivibrator 43 to its reset state after its normal timeperiod in the unstable state allows the brakes to be reapplied for atleast a short time. When the vehicle is moving very slowly, the distancebetween successive signals generated by signal generating means 18 andformed into pulse sequence remains very large and monostablemultivibrator 36 is triggered only at relatively long time intervals.Therefore the output voltage 137 of low pass filter 37 oscillates.Because of these oscillations both the lower threshold value b and theupper threshold value +b .may be constantly passed even for constantspeeds of the vehicle. This would cause monostable multivibrator 43 tobe switched continually, therefore continually activating the magneticvalve which controls the brake power.

In order toprevent such oscillatory applications of brake pressure, thecircuit shown in FIG. 4 is used. This comprises an AND gate 51 which hasa plurality of inputs 48, 48', etc. Voltages are applied to these inputswhich correspond to the rotational velocity of the individual wheels. Itshould be noted that an arrangement as shown in FIG. 3 would in apreferred embodiment of the present invention be connected to eachindividual wheel of the vehicle. Thus a voltage corresponding to thespeed of each wheel is applied, respectively, to inputs 48. In theembodiment shown in FIG. 3 these voltages may be derived from terminal48. If now the speed of all wheels is less than the speed correspondingto the lower threshold value -b (as may occur at vehicle speeds ofapproximately 5 miles per hour), then the conditions for AND gate 51 aremet and AND gate 51 furnishes an output signal which causes Schmitttrigger 52 to change state. It should be noted here that only one ANDgate 51 and one Schmitt trigger 52 is required for each vehicle while,as mentioned above the signal generating means and the logic circuitmeans are supplied for each wheel. The output voltage of amplifier 52 isnowapplied to each coincidence stage of each wheel via terminals 45, 45'et'cyAn output signal of AND gate 51 causes the coincidence requirementsfor coincidence stage 44 to be unfulfilled and it therefore becomesimpossible for logic circuit means 19 to be operative in controlling thebrakes. This is because the magnetic valve which is not shown in thedrawing cannot be switched because no output is supplied at terminal 46.1

The time constants associated with the circuits of the logic circuitmeans are made relatively high in order to prevent oscillatory behaviorin the valves associated with the brake cylinder arrangement 15. Thusthe logic circuit means will also not respond to small decelerationswhich may result from an unevenness of the surface on which the vehicleis rolling.

FIG. 6 shows another advantageous variation of the present invention.Differentiating means 61 are connected to the output of low pass filter37. The output of differentiating means 61 is in turn connected to theinput vof an amplifier 41. Output terminal 48 is also connected with theoutput of low pass filter 37. FIG. 7

' shows the variations of voltage with respect to time at several pointsof the circuit shown in FIG. '6. FIG. 8 shows schematically, thedifferentiating stage shown in FIG. 6. FIG. 8 shows a conventionaloperational amplifier 62 which has an input capacitance 63 and afeedback resistor 65. Connected in series with the input capacitor 63 isa resistance 64 which is a limiting resistance, and connected inparallel with feedback resistor 65 is a filter capacitance 66. Theoutput of operational amplifier 62 constitutes the output of thedifferentiating stage 61. In a conventional operational amplifier suchas amplifier 62, there is a second, non-inverting input. This input issupplied with a DC. voltage which, determines the DC. level of theoutput of stage 61.

Low pass filter 37 as shown in FIG. 6, furnishes the time average of thepulse sequence 236 (FIG. 7) which is available at the output ofmonostable multivibrator 36. This time average value is applied to theinput of differentiating stage 61. Stage 61 is an operational amplifierconstructed as described above. It should only be noted in addition thatthe limiting resistor 64 in its input causes voltage spikes due to noisewhich may appear at the input of the circuit of FIG. 8 to besubstantially suppressed. Filter capacitor 66 causes a damping of highfrequency noise voltages. The resistor 64 and the filter condenser 66must have values relative to elements 63 and 65 that the circuit stillacts as a true differentiator within the frequency region which isrequired for the operation of the present invention. The output voltageof the differentiating stage 61 is shown in the line labelled 261 inFIG. 7. The circuit ofFIG. 6 operates in exact correspondence to thatshown in FIG. 3 and described in detail above.

It should be noted that the above-description has shown severalembodiments wherein brakes are applied or removed in accordance with theoperation required to prevent skidding of the vehicle. It is of coursealso possible that the arrangements set forth herein affect the drivingforce applied to the wheels rather than the braking force appliedthereto. If it is desired to affect the driving force rather than thebraking force, the output signal furnished by the present arrangement isapplied to the clutch between the motor and the driving aide. Theoperation is in other respects completely identical to that describedabove.

It should be noted that an arrangement according to the presentinvention has a number of advantages: First, the signal generating meansare not subject to wear and therefore very high reliability throughoutthe whole life of the arrangement is guaranteed. Further, thearrangement operates practically without time delay so that it maycontrol either the braking or the driving force immediately when a wheelbegins to slide. Furthermore, the fact that the arrangement operatesgenerally in a digital fashion, also insures a relatively great immunityagainst noise voltages. Further, the arrangement in accordance with thisinvention takes consideration of the fact that an increase in the massof the vehicle due to increased loading allows a greater brake ordriving power to be applied to the wheels without causing sliding ofsaid wheels. Further, the arrangement in accordance with this inventionwill operate independent of the fact that the vehicle is either on a drystreet or on an icy path. For vehicle velocities of less than apredetermined value the present arrangement does not respond at allsince such operation is not required at such low speeds.

Without further analysis, tee foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such' adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. An arrangement for furnishing an output signal upon skidding of awheel of a motor vehicle, comprising, in combination, a plurality ofsignal generating means, each operatively associated with the wheel ofsaid motor vehicle, each of said signal generating means furnishing asignal sequence wherein the time interval between sequential signalscorresponds to the rotational velocity of said wheel; and logic circuitmeans each operatively associated with one of said signal generatingmeans for furnishing said output signal when the change in said timeinterval exceeds a predetermined change depending upon the rotationalvelocity of said wheel, each of said logic circuit means comprisingfirst monostable multivibrator means, low pass filter means connected tothe output of said monostable multivibrator means, additional circuitmeans for furnishing a differentiated signal corresponding to thederivative with respect to time of the output of said low pass filtermeans in the absence of said additional circuit means, threshold meansconnected to receive said differentiated signal, and furnishing athreshold signal when said differentiated signal differs by more than apredetermined difference from a predetermined level, and secondmonostable multivibrator means connected to the output of said thresholdmeans.

2'. An arrangement as set forth in claim 1, wherein said threshold meansfurnishes a first threshold signal at a first threshold output when saiddifferentiated signal is lower than said predetermined level by apredetermined difference, and a second threshold signal at a secondthreshold output when said differentiated signal is higher than saidpredetermined level by a predetermined difference; and wherein saidsecond monostable multivibrator has a first input connectedto said firstthreshold output and a second input connected to said second thresholdoutput and a second monostable output.

3. An arrangement as set forth in claim 1, further comprisingcoincidence means having a first and second coincidence input and acoincidence output; means connecting said second monostable output tosaid first coincidence input; and wherein the output of said coincidencemeans constitutes said output signal.

4. An arrangement as set forth in claim 3, further comprising means forfurnishing a plurality of voltages, each corresponding to the speed ofone of said wheels of said vehicle; and AND gate means having a numberof inputs corresponding to said plurality of voltages, each of saidinputs being connected to receive one of said voltages, said AND gatemeans further having an AND gate output.

5. An arrangement as set forth in claim 4, wherein said means forfurnishing a plurality of voltages, each corresponding to the speed ofone wheel, comprise a plurality of interconnecting means, eachinterconnecting the output of one of said low pass filter means to acorresponding AND gate input.

6. An arrangement as set forth in claim 4, wherein said signalgenerating means and said logic circuit means each comprise a pluralityof means, each of said plurality of means being operatively associatedwith one of said wheels of said motor vehicle; further comprisinginterconnecting means interconnecting said AND gate output with thesecond coincidence input of each of said plurality of means.

7. An arrangement as set forth in claim 6, wherein said interconnectingmeans comprise a Schmitt trigger connected with said AND gate output.

8. An arrangement as set forth in claim 6, further comprising a Schmitttrigger circuit connected to the output of each of said signalgenerators.

9. An arrangement as set forth in claim 8 further comprising additionaldifferentiating means, each connected to the output of one of saidSchmitt trigger circuits.

10. An arrangement as set forth in claim 9, wherein said firstmonostable multivibrator has a first input for switching said monostablemultivibrator to the unstable stage and a second input for a adjustingthe time interval said first monostable multivibrator is in saidunstable state; wherein said additional circuit means compriseintegrator means connected between the output of said low pass filtermeans and said second input of said first monostable multivibrator; andwherein said said additional circuit means comprise a differentiatingcircuit connected to the output of said low pass filter means.

12. An arrangement as set forth in claim 1 1, wherein saiddifferentiating circuit comprises an operational amplifier having afeedback resistor and an input capacitor.

13. An arrangement as set forth in claim 12, further comprising adamping resistor connected in series with said input capacitor.

14. An arrangement as set forth in claim 12, further comprising a filtercapacitor connected in parallel with said feedback resistor.

15. An arrangement as set forth in claim 12, further comprisingdifferential amplifier means connected to the output of saiddifferentiating circuit.

16. An arrangement as set forth in claim 1, wherein each of said signalgenerating means comprise a magnetic wheel having projections,mechanically coupled to the corresponding wheel of said motor vehicle,and sensing means for sensing said projection mechanically connectedwith the chassis of said motor vehicle.

17. An arrangement as set forth in claim 1, wherein said threshold meanscomprise an operational amplifier.

18. An arrangement as set forth in claim 1, wherein said threshold meanscomprise a Schmitt trigger.

19. An arrangement for furnishing an output signal upon skidding of awheel of a motor vehicle, comprising, in combination, signal generatingmeans operatively associated with a wheel of said motor vehicle, each ofsaid signal generating means furnishing a signal sequence wherein thetime interval between sequential signals corresponds to the rotationalvelocity of said wheel; and logic circuit means operatively associatedwith said signal generating means for furnishing saidoutput signal whenthe change in said time interval exceeds a predetermined changedepending upon the rotational velocity of said wheel, said logic circuitmeans comprising: first monostable multivibrator means having a firstand second input and an output, a signal at said first input switchingsaid first monostable multivibrator means into the unstable state, saidfirst monostable multivibrator means remaining in said unstable statefor a time depending upon the signal at said second input; low passfilter means connected to the output of said first monostablemultivibrator means; and integrator means connected between the outputof said low pass filter means and said second input of said firstmonostable multivibrator means, a signal having an amplitude exceeding apredetermined amplitude at the output of said low pass filter meansconstituting said output signal.

1. An arrangement for furnishing an output signal upon skidding of awheel of a motor vehicle, comprising, in combination, a plurality ofsignal generating means, each operatively associated with the wheel ofsaid motor vehicle, each of said signal generating means furnishing asignal sequence wherein the time interval between sequential signalscorresponds to the rotational velocity of said wheel; and logic circuitmeans each operatively associated with one of said signal generatingmeans for furnishing said output signal when the change in said timeinterval exceeds a predetermined change depending upon the rotationalvelocity of said wheel, each of said logic circuit means comprisingfirst monostable multivibrator means, low pass filter means connected tothe output of said monostable multivibrator means, additional circuitmeans for furnishing a differentiated signal corresponding to thederivative with respect to time of the output of said low pass filtermeans in the absence of said additional circuit means, threshold meansconnecTed to receive said differentiated signal, and furnishing athreshold signal when said differentiated signal differs by more than apredetermined difference from a predetermined level, and secondmonostable multivibrator means connected to the output of said thresholdmeans.
 2. An arrangement as set forth in claim 1, wherein said thresholdmeans furnishes a first threshold signal at a first threshold outputwhen said differentiated signal is lower than said predetermined levelby a predetermined difference, and a second threshold signal at a secondthreshold output when said differentiated signal is higher than saidpredetermined level by a predetermined difference; and wherein saidsecond monostable multivibrator has a first input connected to saidfirst threshold output and a second input connected to said secondthreshold output and a second monostable output.
 3. An arrangement asset forth in claim 1, further comprising coincidence means having afirst and second coincidence input and a coincidence output; meansconnecting said second monostable output to said first coincidenceinput; and wherein the output of said coincidence means constitutes saidoutput signal.
 4. An arrangement as set forth in claim 3, furthercomprising means for furnishing a plurality of voltages, eachcorresponding to the speed of one of said wheels of said vehicle; andAND gate means having a number of inputs corresponding to said pluralityof voltages, each of said inputs being connected to receive one of saidvoltages, said AND gate means further having an AND gate output.
 5. Anarrangement as set forth in claim 4, wherein said means for furnishing aplurality of voltages, each corresponding to the speed of one wheel,comprise a plurality of interconnecting means, each interconnecting theoutput of one of said low pass filter means to a corresponding AND gateinput.
 6. An arrangement as set forth in claim 4, wherein said signalgenerating means and said logic circuit means each comprise a pluralityof means, each of said plurality of means being operatively associatedwith one of said wheels of said motor vehicle; further comprisinginterconnecting means interconnecting said AND gate output with thesecond coincidence input of each of said plurality of means.
 7. Anarrangement as set forth in claim 6, wherein said interconnecting meanscomprise a Schmitt trigger connected with said AND gate output.
 8. Anarrangement as set forth in claim 6, further comprising a Schmitttrigger circuit connected to the output of each of said signalgenerators.
 9. An arrangement as set forth in claim 8 further comprisingadditional differentiating means, each connected to the output of one ofsaid Schmitt trigger circuits.
 10. An arrangement as set forth in claim9, wherein said first monostable multivibrator has a first input forswitching said monostable multivibrator to the unstable stage and asecond input for a adjusting the time interval said first monostablemultivibrator is in said unstable state; wherein said additional circuitmeans comprise integrator means connected between the output of said lowpass filter means and said second input of said first monostablemultivibrator; and wherein said means for furnishing a plurality ofvoltages, each corresponding to the speed of one wheel, compriseconnecting means connecting the output of said integrator means to acorresponding one of said AND gate inputs.
 11. An arrangement as setforth in claim 1, wherein said additional circuit means comprise adifferentiating circuit connected to the output of said low pass filtermeans.
 12. An arrangement as set forth in claim 11, wherein saiddifferentiating circuit comprises an operational amplifier having afeedback resistor and an input capacitor.
 13. An arrangement as setforth in claim 12, further comprising a damping resistor connected inseries with said input capacitor.
 14. An arrangement as set forth inclaim 12, further comprising a filter capAcitor connected in parallelwith said feedback resistor.
 15. An arrangement as set forth in claim12, further comprising differential amplifier means connected to theoutput of said differentiating circuit.
 16. An arrangement as set forthin claim 1, wherein each of said signal generating means comprise amagnetic wheel having projections, mechanically coupled to thecorresponding wheel of said motor vehicle, and sensing means for sensingsaid projection mechanically connected with the chassis of said motorvehicle.
 17. An arrangement as set forth in claim 1, wherein saidthreshold means comprise an operational amplifier.
 18. An arrangement asset forth in claim 1, wherein said threshold means comprise a Schmitttrigger.
 19. An arrangement for furnishing an output signal uponskidding of a wheel of a motor vehicle, comprising, in combination,signal generating means operatively associated with a wheel of saidmotor vehicle, each of said signal generating means furnishing a signalsequence wherein the time interval between sequential signalscorresponds to the rotational velocity of said wheel; and logic circuitmeans operatively associated with said signal generating means forfurnishing said output signal when the change in said time intervalexceeds a predetermined change depending upon the rotational velocity ofsaid wheel, said logic circuit means comprising: first monostablemultivibrator means having a first and second input and an output, asignal at said first input switching said first monostable multivibratormeans into the unstable state, said first monostable multivibrator meansremaining in said unstable state for a time depending upon the signal atsaid second input; low pass filter means connected to the output of saidfirst monostable multivibrator means; and integrator means connectedbetween the output of said low pass filter means and said second inputof said first monostable multivibrator means, a signal having anamplitude exceeding a predetermined amplitude at the output of said lowpass filter means constituting said output signal.